A large number of cytokines participate in the inflammatory response, including IL-1, IL-6, IL-8 and TNF-α. The overproduction of cytokines such as IL-1 and TNF-α is implicated in a wide variety of diseases, including inflammatory bowel disease, rheumatoid arthritis, psoriasis, multiple sclerosis, endotoxin shock, osteoporosis, Alzheimer's disease, and congestive heart failure. See e.g. Henry et al., Drugs Fut., Vol. 24 (1999), at pp. 1345-1354; and Salituro et al., Curr. Med. Chem., Vol. 6 (1999), at pp. 807-823. Evidence in human patients indicates that protein antagonists of cytokines are effective in treating chronic inflammatory diseases, such as, for example, monoclonal antibody to TNF-α (Enbrel) (see Rankin et al., Br. J. Rheumatol., Vol 34 (1995), at pp. 334-342), and soluble TNF-α receptor-Fc fusion protein (Etanercept) (see Moreland et al., Ann. Intern. Med., Vol. 130 (1999), at pp. 478-486).
The biosynthesis of TNF-α occurs in many cell types in response to an external stimulus, such as, for example, a mitogen, an infectious organism, or trauma. Important mediators of TNF-α production are the mitogen-activated protein (MAP) kinases, including p38 kinase (p38). Activation of p38 requires dual phosphorylation by an upstream MAP kinase (MKK3 and MKK6) on threonine and tyrosine within a Thr-Gly-Tyr motif characteristic of p38 isozymes. The p38 kinase is an upstream kinase of mitogen-activated protein kinase-activated protein kinase-2 (MAPKAP K2 or MK2). See Freshney et al., Cell, Vol. 78 (1994), at pp. 1039-1049.
MK2 is a protein that appears to be predominantly regulated by p38 in cells. In fact, MK2 was the first substrate of p38α to be identified, and in vitro phosphorylation of MK2 by p38α is required for MK2 activation. MK2, in turn, phosphorylates substrates including, but not limited to, heat shock protein 27 (HSP27), lymphocyte-specific protein 1 (LAP-1), leukocyte-specific protein-1 (LSP-1), 5-lipoxygenase (5-LO), cAMP response element-binding protein (CREB), ATF1, serum response factor (SRF), tyrosine hydroxylase, and most importantly, adenosine and uridine-rich element (ARE) binding proteins. ARE binding proteins regulate the mRNA stability of inflammatory mediators such as TNFα and COX-2.
Targeted mutations have been introduced into the mouse MK2 gene that resulted in the generation of MK2-deficient mice. See Kotlyarov et al, Nat. Cell Biol., Vol. 1 (1999), at pp. 94-97. These MK2-deficient mice exhibited increased stress resistance to LPS-induced endoxic shock and had a better survival rate compared to mice that retained the MK2 gene. See id. Isolated splenocytes from these mice challenged with LPS had reduced levels of TNFα, IL-1β, IL-6 and IFNγ. See id. More recently, Lehner et al. reported that MK2-deficient mice showed increased susceptibility to Listeria moocytogenes infection and concluded that MK2 had an essential role in host defense against intracellular bacteria, probably through the regulation of TNFα and IFNγ, two of the cytokines required for the activation of antibacterial effector mechanisms. See Lehner et al., J. Immunol., Vol. 168 (2002), at pp. 4667-4673. Moreover, since MK2 is located immediately downstream of p38 in the p38 signaling pathway, it is recognized that MK2 could act as a focal point for more selectively modulating the inflammatory pathway thereby reducing the possibility of undesirable side effects.
Pyrazolo[1,5-a]pyrimidine derivatives have been disclosed in WO2004076458(A1) and described as having kinase inhibiting activity.
New compounds and methods of modulating the activity of kinases, including MK2, would be desirable in the treatment of diseases and disorders that are mediated by cytokines, such as TNFα. It would be even more desirable to provide MK2 inhibitors that have improved potency and reduced undesirable side effects.